1. Field of the Invention
The present invention generally relates to the field of mobile positioning. More specifically, the present invention relates to systems and methods for wireless Location Based Services.
2. Description of Related Art
Location-Based Services (LBSs) has emerged as an essential public safety feature of cellular systems, referring to the geographic coordinates of a mobile user, in part to an order issued by the Federal Communications Commission (FCC) in 1996—Emergency 911 (or E-911). Moreover, the wireless location technology has migrated into various profitable industries such as mobile advertising, asset tracking, fleet management, and location-based wireless access security.
In military applications, situation awareness (SAW) technology is needed to allow the future net-centric Warfighter to operate in squads or sub-squad teams, requiring dedicated wireless communications networks and location finding technology for operation effectiveness. Wireless, command and control, and sensor networking technology that provide individual soldiers with a tactical network-centric capability and enable small units to maintain precision location of its team members would have a tremendous impact on the military and its operations. A key component of this needed technology is that the individual soldier system is designed to provide the dismounted soldier with wireless location tracking technology in order for fast rescue missions.
Generally, wireless location technologies fall into two main categories: mobile-based and network-based.
In mobile-based outdoor location systems, the mobile station typically determines its location from signals received by a few base stations or from the Global Positioning Satellite (GPS) system. GPS methods provide global location information and have a relatively high degree of accuracy, however transmitted signal strengths deteriorate tremendously in buildings and around outdoor structures such as trees, bridges, and concrete objects. In military operations, outdoor obstructions continue to plague a central command control that is charged with tracking individual troop movement at all times.
Network-based location technology, on the other hand, relies on some existing WLAN or mobile Ad hoc networks to determine the position of a user. Ad-hoc networks are defined as networks formed by users or devices wishing to communicate, without the necessity or existence of any infrastructure previously established between potential network members. Ad-hoc communication can take place in different scenarios and is independent of any specific device, wireless transmission technology, network, or protocol. Ad-hoc networks can significantly vary in size depending on application. For example, the network can contain two nodes or thousands of nodes that exchange data. Another feature of ad-hoc networks is that nodes are free to enter or leave the network at any time.
To date, the most developed wireless location technologies have been in the areas of GPS, advanced U.S. scientific, and technical capabilities by means of Global System for Mobile Communications (GSM), and Code Division Multiple Access (CDMA) in worldwide commercial applications such as transportation management, directional finding software, and emergency services. In cellular service there are two main competing network technologies: GSM and CDMA. Cellular carriers including Sprint PCS™, Cingular Wireless™, Verizon™ and T-Moblie™ use one or the other.
It is generally accepted that WLAN and sensor (or beacon) networks are best implemented for indoor use while outdoor Location Based Services are well-established with respect to GPS and GSM positioning. In terms of indoor positioning, sensor (or beacon) networks have a longer history of research with a number of different frequency bands including ultrasound, infrared, and Ultra-Wideband. However, one key drawback to sensor networks are the limited coverage areas they support due to various frequency limitations. Therefore, these technologies are all geared toward very small regions, sometimes referred to as Personal Area Networks (PANs). In order to provide wider coverage areas, these networks would require a high concentration of sensors, thereby hindering the cost effectiveness of deploying wide-scale sensor networks.
Although WLAN positioning has attracted much research attention in recent years, many challenges exist. According to Sun et al. (“Signal Processing Techniques in Network Aided Positioning: A survey of state-of-the-art positioning designs” IEEE Signal Processing Magazine, Vol. 22, Issue 4, pp. 12-23 (2005)), different network topologies pose various challenges in mobile positioning. Signal strength and accuracy are other challenges with respect to WLAN indoor positioning. Most WLAN indoor positioning systems are based on received signal strength (or RSS) since such measurements are part of normal operation.
Signal processing techniques for location estimation in 802.11 based wireless networks typically include client-based systems and client-assisted systems. In client-based systems, a model is initially constructed based on received signal strengths within a target area. The position of a mobile device is determined by comparing received signal strengths from each access point with the model. Most of the computational processing for client-based systems is performed remotely, while client-assisted location systems draw resources from client terminals, access points, and sniffing devices to locate the clients in WLAN.
To date, the data collection process for WLAN signal strength models entails a crude method of walking, driving, or flying throughout a region of Wireless Access Points (WAPs) with a laptop running WLAN detection software. One method includes “war-driving” and is practiced by hobbyists, hackers, and security analysts worldwide. WLAN detection software stores the radio beacon signal of WAPs near the moving laptop. Thus, the fixed WAPs can be used as frame of reference coordinates or as triangulation points for newly arriving IEEE 802.11 devices. Examples of software and hardware that may be used for war-driving include: Netstumbler V.4.0, Dell Laptop Latitude C500/600 (running Windows 98 or higher), Compaq WL 110 Wireless PC Card, DeLorme Street Atlas 2004 USA, Dell TrueMobile 1150 WLAN Adapter, M.S. MapPoint 2004, DeLorme Earthmate® GPS w/USB port, Earthmate® Hyperformance GPS Receiver w/RS232 connector, MaxRAD™ 2.4 GHz MIG Omnidirectional tape mount antenna. In one example, a beacon database of three thousand wireless access points was collected on a drive throughout the city of Rockville, Md., running Netstumbler, a WLAN card, and an omni-directional antenna retrieved the IEEE 802.11 RF beacon signals. One major drawback of war-driving techniques, however, is that such processes are extremely time consuming (e.g., on the order of eight hours per 5 square miles).
While various approaches for combining one or more LBS technologies have been proposed, most are directed toward outdoor applications focused on the cellular or GPS market. There have been very few commercial applications that utilize WLAN Location Based Services. While U.S. Pat. No. 7,130,646 to Wang discloses WLAN-aided Global Positioning Systems, the invention does not provide seamless indoor and outdoor tracking and is limited to WLAN RSSI measurements. In addition, Wang requires an access point (or beacon) database and lookup table to merely determine a “best-matching” position of the device.
Moreover, while cellular networks, Global Positioning Systems (GPS) and wireless E911 services generally address the issue of location finding, these technologies cannot provide an indoor geo-location because they face various electrical magnetic limitations (e.g., radio interference, penetration loss, and multi-path conditions). At the same time, current indoor positioning techniques lack precision and accuracy.
The inventor has recognized that there exists a need in the art to provide a system and method for accurate positioning of WLAN-based wireless devices. The inventor has also recognized that there also exists a need to provide a system, method, and device for seamless indoor and outdoor tracking utilizing WLAN and/or GPS signals. Furthermore, it has become apparent to the inventor that there exists a need to provide improved two and three dimensional rendering of mobile device position.